The removal of fine particles from a gas, is required in a large number of applications, such as in the removal of particulate contaminants from the exhausts of power sources. Several devices such as cyclones, venturi scrubbers, and fabric filters, can efficiently remove larger particles such as those above about 5 micron diameter. However, devices are not available for efficiently removing smaller particles.
Fine particles can be removed by using acoustic energy to vibrate particles to bring them close to one another so they stick together. Such acoustic agglomeration is a proven process for removal of fine particles, but previous attempts have not been cost effective. Most attempts have involved the application of acoustic energy of frequencies that produce large particle vibrations, but without regard to the dimensions of the pipe or chamber in which the gas was moving, so that large amounts of energy were required to produce only moderately intense acoustic fields. Another system, described in U.S. Pat. No. 2,215,484 by St. Clair, uses a technique wherein particle-ladden gas passes along the length of a chamber while a sound wave resonant to the length of the chamber is applied, to cause particles to agglomerate at the locations of minimum pressure of the standing wave pattern, in the manner of the well known Kundt dust-tube experiment. This technique will not simultaneously agglomerate particles of a wide range of sizes, which is a disadvantage because a wide range of fine particles sizes are encountered in many applications.